Minecraft 1.12.2, Minecraft 18w08b, Minecraft 18w09a, Minecraft 18w10a, Minecraft 18w11a
Windows 10, Java version 8 update 91. (I don't believe this issue is specific to the environment.)
When using the /say command to say the name of an entity, e.g.
It is always the case, that the name(s) said are in the colour of the team they are assigned to.
When using the "/tellraw" command however, e.g.
"/tellraw @s [
The team colors are only applied if the selector returns more than one entity. This is problematic when using team colors as a way to format parts of a longer /tellraw command.
The results of the commands can be seen on the attached images.
Doesn't only affect team color, all components except plain text seems to be affected. See comments for more info.